Solid state image sensor with extended spectral response

ABSTRACT

Various embodiments are directed to an image sensor that includes a first sensor portion and a second sensor portion coupled to the first sensor portion. The second sensor portion may be positioned relative to the first sensor portion so that the second sensor portion may initially detect light entering the image sensor, and some of that light passes through the second sensor portion and is be detected by the first sensor portion. In some embodiments, the second sensor portion may be configured to have a thickness suitable for sensing visible light. The first sensor portion may be configured to have a thickness suitable for sensing IR or NIR light. As a result of the arrangement and structure of the second sensor portion and the first sensor portion, the image sensor captures substantially more light from the light source.

RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §119 to ProvisionalApplication No. 62/270,547 entitled “SOLID STATE IMAGE SENSOR WITHEXTENDED SPECTRAL RESPONSE,” filed Dec. 21, 2015, the contents of whichis expressly incorporated by reference in its entirety.

BACKGROUND

Field of Invention

This disclosure relates to an image sensor, and specifically to an imagesensor having an extended spectral range.

Description of Related Technology

Image processing devices, such as digital cameras, smartphones or tabletcomputers, rely on image sensors to capture images. Image sensorsreceive light and convert that light into electrical signals. The imageprocessing devices then transform these electrical signals into digitalimages.

Different types of image sensors are currently available. For example,image processing devices typically utilize either afrontside-illumination (FSI) image sensor or a backside-illumination(BSI) image sensor. An FSI image sensor is typically oriented such thatlight enters the top of the FSI image sensor and passes through ametal-interconnect layer before striking the light-sensing surface. Incontrast, BSI image sensors are oriented to allow light to enter fromthe top of the BSI image sensor and to strike a light-sensing surfacewithout passing through the metal/wiring layer of the BSI wafer. Whileeach of the FSI and BSI image sensors have favorable imagingcharacteristics, they both may have limited spectral responses.Accordingly, there is a need for an image sensor having a greaterspectral response than either a FSI or BSI image sensor.

SUMMARY OF THE INVENTION

The systems, methods, and devices of the invention each have severalaspects, no single one of which is solely responsible for its desirableattributes. Without limiting the scope of this invention as expressed bythe claims which follow, some features will now be discussed briefly.

Various embodiments include a method for assembling an image sensor. Insome embodiments, the method may include forming a firstmetal-interconnect layer on a first sensor portion, forming a secondmetal-interconnect layer on a second sensor portion, forming a firstlight pipe within the first metal-interconnect layer, forming a secondlight pipe within the second metal-interconnect layer, positioning thefirst sensor portion relative to the second sensor portion such that thefirst light pipe and the second light pipe are aligned and orientedabout a common axis, and bonding the first metal-interconnect layer withthe second metal-interconnect layer.

In some embodiments, the method may further include coupling a colorfilter to the second sensor portion and coupling a micro-lens to thecolor filter. In some embodiments, bonding the first metal-interconnectlayer with the second metal-interconnect layer may cause the first lightpipe and the second light pipe to form a cavity about the common axis.In some embodiments, the cavity may be configured to enable light topass from the second photodetector, through a combinedmetal-interconnect layer that includes the first metal-interconnectlayer and the second metal-interconnect layer, and to the firstphotodetector. In some embodiments, bonding the first metal-interconnectlayer with the second metal-interconnect layer may further includebonding the first light pipe with the second light pipe. In someembodiments, a thickness of the first sensor portion may be at leastseven micrometers.

In some embodiments, the method may further include reducing a thicknessof the second sensor portion such that the reduced thickness of thesecond sensor portion enables infrared or near-infrared light to passthrough the second sensor portion. The thickness of the second sensorportion may also be reduced to between three micrometers and fivemicrometers, inclusive.

In some embodiments, forming the first light pipe may include formingthe first light pipe in the first metal-interconnect layer with respectto a photodetector embedded in the first sensor portion, and forming thesecond light pipe may include forming the second light pipe in thesecond metal-interconnect layer with respect to a photodetector embeddedin the second sensor portion. Further, positioning the first sensorportion in relation to the second sensor portion may further includealigning the photodetector of the first sensor portion with thephotodetector of the second sensor portion.

Various embodiments may include an image sensor that includes a firstsensor portion and a second sensor portion coupled to the first sensorportion. In some embodiments, the first sensor portion may include afirst photodetector, a first metal-interconnect layer, and a first lightpipe. In such embodiments, the second sensor portion may include asecond photodetector, a second metal-interconnect layer, and a secondlight pipe. As such, the first metal-interconnect layer may be bonded tothe second metal-interconnect layer to form a combinedmetal-interconnect layer.

In some embodiments, a thickness of the first sensor portion may be atleast seven micrometers. In some embodiments, a thickness of the secondsensor portion may be no more than five micrometers. In someembodiments, the image sensor may also include a color filter and amicro-lens. In some embodiments, the first light pipe may be formedwithin the first metal-interconnect layer, and the second light pipe maybe formed within the second metal-interconnect layer.

In some embodiments, the first metal-interconnect layer may be bonded tothe second metal-interconnect layer such that the first photodetectoraligns with the second photodetector about a common axis. The firstlight pipe may also be aligned with the second light pipe about thecommon axis.

In some embodiments, the first light pipe may be positioned with respectto the second light pipe to form a cavity within the combinedmetal-interconnect layer between the first photodetector and the secondphotodetector. The cavity may be configured to allow light to pass fromthe second photodetector of the second sensor portion, through thecombined metal-interconnect layer, and to the first photodetector of thefirst sensor. In some embodiments, the light may originate from a commondirection. The light may also include at least one of near-infraredlight or infrared light.

In some embodiments, the first sensor image may further include a firstplurality of epitaxial layers, and each epitaxial layer of the firstplurality of epitaxial layers may have a distinct doping concentration.Further, the first plurality of epitaxial layers may be arranged withinthe first sensor portion based on respective doping concentrations ofthe first plurality of epitaxial layers.

In some embodiments, the second sensor portion may also include a secondplurality of epitaxial layers, and each epitaxial layer of the secondplurality of epitaxial layers may have a distinct doping concentration.Further, the second plurality of epitaxial layers may be arranged withinthe second sensor portion based on respective doping concentrations ofthe second plurality of epitaxial layers, and an arrangement of thesecond plurality of epitaxial layers within the second sensor portionmay be inverse of an arrangement of the first plurality of epitaxiallayers within the first sensor portion.

Various embodiments may include an image processing device. In someembodiments, the image processing device may include an image sensorthat includes a first portion, a second portion, and a combinedmetal-interconnect layer. The image processing device may also include amemory and a processor coupled to the memory and coupled to the imagesensor. The first portion of the image sensor may include a firstphotodetector and a first light pipe. The second portion of the imagesensor may include a second photodetector aligned with the firstphotodetector about a common axis and a second light pipe positioned inrelation to the first light pipe. The combined metal-interconnect layermay be coupled to the first portion of the image sensor and to thesecond portion of the image sensor. In some embodiments, the firstphotodetector may be configured to receive at least a first portion oflight from a light source, and the second photodetector may beconfigured to receive at least a second portion of the light from thelight source.

In some embodiments, the first photodetector may be configured toconvert the first portion of light into a first electrical signal, thesecond photodetector may be configured to convert the second portion ofthe light into a second electrical signal, and the combinedmetal-interconnect layer may be configured to drive the first electricalsignal and the second electrical signal to the processor. In someembodiments, the image sensor may be arranged such that, when the secondportion of the image sensor is proximal to the light source, the atleast second portion of the light passes through the second portion ofthe image sensor before the at least first portion of the light passesthrough the first portion of the image sensor. In some embodiments, thefirst portion of the light may include at least one of infrared light ornear-infrared light, and the second portion of the light may includevisible light.

In some embodiments, the memory may include processor-executableinstructions that, when executed by the processor, cause the processorto perform operations that include generating a first digital signalfrom the first electrical signal, generating a second digital signalfrom the second electrical signal, and generating a combined digitalsignal from the first digital signal and the second digital signal. Insome embodiments, the memory may include processor-executableinstructions that, when executed by the processor, cause the processorto perform operations that further include generating a digital imagebased at least in part on the combined digital signal.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing aspects and many of the attendant advantages will becomemore readily appreciated as the same become better understood byreference to the following detailed description, when taken inconjunction with the accompanying drawings, wherein:

FIG. 1A is a component diagram showing a cross-section view of afrontside-illuminated image sensor.

FIG. 1B is a component diagram showing a cross-section view of abackside-illuminated image sensor.

FIG. 2 is a component block diagram showing a cross-section view of animage sensor, according to some embodiments.

FIG. 3 is a component block diagram showing another cross-section viewof an image sensor that includes certain features of a front-illuminatedsensor and certain features of a backside-illuminated sensor, as well asadditional features, according to some embodiments.

FIGS. 4A-4F are component block diagrams illustrating an example methodof assembling an image sensor, according to some embodiments.

FIG. 5 is a component block diagram showing a top view of the imagesensor, according to some embodiments.

FIGS. 6A and 6B are component block diagrams illustrating alternativewafers for use in assembling an image sensor, according to someembodiments.

FIG. 7 is a component block diagram illustrating an example of an imageprocessing device suitable for use with some embodiments.

DETAILED DESCRIPTION

As described herein, some components of an image sensor (e.g., an FSI orBSI image sensor) may sometimes be referred to as positioned “above,”“on top of,” “underneath, “below,” or similar terminology in relation tosome other components. For ease of description, spatial relationsbetween components in an image sensor may be described in relation tothe “top” and “bottom” of the image sensor. In some embodiments, the“top” of an image sensor may correspond with the point at which lightinitially enters the image sensor. Accordingly, the “bottom” of theimage sensor may be on the opposite side of the image sensor than thetop of the image sensor. Thus, a first component of an image sensor thatis closer to the top of the image sensor than a second may be describedas being “on top of” or “above” the second component.

The terms “sensor element” is used herein to refer to a basic componentof an image sensor that is configured to capture light information.Specifically, a sensor element may be configured to capture a portion ofa photographic object such that a representation of the entirephotographic image (or a larger portion) may be captured using multiplesensor elements of the image sensor. An image sensor may be described asincluding or having one or more sensor elements arranged as atwo-dimension array or matrix. This two-dimensional array may correspondwith a particular resolution of a related digital image, and more sensorelements typically correspond with higher-resolution digital images. Forexample, an image processing device (e.g., a digital camera) with animage sensor having a 640×480 array of sensor elements (e.g., a 0.3megapixel image sensor) may capture lower resolution digital images thananother image processing device with an image sensor having a 4000×3000array of sensor elements (e.g., a 12 megapixel image sensor). Anyreference to an image sensor having a certain number of sensor elementsis simply for ease of description and is not intended to limit any imagesensor to have any particular number of sensor elements, unlessotherwise indicated.

As noted above, the silicon wafers used in a conventionalbackside-illumination (BSI) image sensor may be ground to be thin enoughsuch that light enters from the front of the BSI wafer and strikes alight receiving surface without passing through the metal/wiring layerof the BSI image sensor. Because light does not pass through the wiringin a BSI wafer, light is not scattered or obstructed to the same degreeas observed in frontside-illumination (FSI) image sensors. Thus, BSIimage sensors generally experience better performance when detectingvisible light than FSI image sensors. However, because BSI image sensorsare thinner than FSI wafers (e.g., less than three micrometers versusgreater than seven micrometers, respectively), BSI image sensors do notdetect near-infrared (“NIR”) or infrared (“IR”) light as well as FSIimage sensors due to the relatively longer wavelengths of NIR/IR light.

In overview, various embodiments provide for an image sensor configuredto sense visible light on par with a BSI image sensor, while at the sametime also being configured to sense IR or NIR light as well as an FSIimage sensor. In such embodiments, the image sensor may include a firstsensor portion (which may also be referred to as a first image sensor)configured to function similar to an FSI image sensor within the imagesensor. Further, the image sensor may include a second sensor portion(which may be referred to as a second image sensor) configured tofunction similar to a BSI image sensor and coupled to the first sensorportion. In various embodiments, the image sensor may be configured suchthat the second sensor portion is positioned on top of the first sensorportion, “top” being used refer to a position such that light may enterthe second sensor portion and be detected, and some of that light maypass through the second sensor portion and may be detected with thefirst sensor portion. In some embodiments, the second sensor portion maybe configured to have a thickness suitable for sensing visible light,such as by performing wafer thinning or grinding. The first sensorportion may be configured to have a thickness suitable for sensing IR orNIR light, which may not require wafer grinding or may require a lesserdegree of grinding. By positioning the second sensor portion above thefirst sensor portion such that each image sensor is able to capture somelight from the same source (e.g., from the same direction), the overalllight captured by the image sensor may be improved. Various embodimentsfurther relate to methods for fabricating such an image sensor.

In some embodiments, the first sensor portion and the second sensorportion of the image sensor may have one or more sensor elements. Thefirst sensor portion and the second sensor portion may be physicallycoupled or affixed together in such a way that each sensor element ofthe first sensor portion is aligned with a corresponding sensor elementof the second sensor portion. Specifically, each sensor element of thefirst sensor portion may be positioned below a corresponding sensorelement of the second sensor portion. In an example in which each of thefirst sensor portion and the second sensor portion has two sensorelements (e.g., a 2×1 sensor array), a first sensor element of the firstsensor portion may be aligned with a corresponding first sensor elementof the second sensor portion, and a second sensor element of the firstsensor portion may be aligned with a second corresponding sensor elementof the second sensor image.

In some embodiments, the alignment of sensor elements of the first andsecond sensor portions may include aligning photodetectors and lightpipes in the first and second sensor portions of the image sensor (e.g.,as discussed with reference to FIG. 2), which may ensure that light fromthe same source is captured or sensed by corresponding sensor elementsin the image sensor. In such embodiments, this configuration of theimage sensor may enable a photodetector in the second sensor portion toreceive visible light from a source and may also enable a correspondingphotodetector in the first sensor portion to receive NIR or IR lightfrom the same source. The configuration and alignment of the first andsecond sensor portions of the image sensor facilitates the capture oflight from the same source using two sets of photodetectors, and as aresult, the digital images created from the light captured with thesephotodetectors may have a higher degree of detail, especially inlow-light situations.

In some embodiments, the first sensor portion and the second sensorportion of the image sensor may be physically coupled or affixedtogether by bonding the metal-interconnect layers of each of the firstand second sensor portions into an metal-interconnect layer. Forexample, the metal-interconnect layers of the first and second sensorportions may be coupled by applying a metal-oxide adhesive. In suchembodiments, photodetectors in both of the first and second sensorportions may share the combined metal-interconnect layer to sendelectrical signals generated from captured light to imaging processingcomponents coupled to the image sensor.

In embodiments described herein, certain references to an image sensoras having a “first sensor portion” (or a “first image sensor”) or a“second sensor portion” (or a “second image sensor”) is merely for easeof labeling and description. As such, the description of an image sensoras a “first sensor portion” or a “second image sensor” is not intendedto be limiting.

Various embodiments will be described in detail with reference to theaccompanying drawings. Generally, the same reference numbers will beused throughout the drawings to refer to the same or like part.References made to particular examples and implementations are forillustrative purposes, and are not intended to limit the scope of theinvention or the claims.

FIG. 1A is a side view of a cross-section of an example of an embodimentof an FSI image sensor 100 that illustrates certain features. In thisexample, the FSI image sensor 100 includes a substrate layer 102, anepitaxial layer 104, a metal-interconnect layer 108, one or more colorfilters (e.g., color filters 110 a and 110 b), and one or moremicro-lenses (e.g., micro-lenses 112 a and 112 b).

The FSI image sensor 100 is oriented such that light (e.g., light 118 aor 118 b) enters from the top of the FSI image sensor 100. In theexample illustrated in FIG. 1A, light 118 a or 118 b enters the FSIimage sensor 100 via the micro-lenses 112 a and 112 b, which focus thelight 118 a or 118 b. The light 118 a and 118 b then passes through thecolor filters 110 a-b. In particular, the color filters 110 a and 110 bblock light in certain wavelengths (e.g., certain colors) so that lightthat passes through the color filters may have a particular color or maybe associated with a particular range of wavelengths or colors.

After being focused by the micro-lenses 112 a and 112 b and filtered bythe color filters 110 a and 110 b, the light 118 a or 118 b passesthrough the metal-interconnect layer 108—usually through one or morelight pipes 116 a and 116 b—to be received by the photodetectors 114 aand 114 b included in the epitaxial layer 104. The light pipes 116 a and116 b may be embedded in the metal-interconnect layer 108 and mayfacilitate the passage of the light 118 a and 118 b through themetal-interconnect layer 108 by restricting the light to within thelight pipes 116 a and 116 b. As a result, portions of the light 118 aand 118 b may avoid passing directly through the metal-interconnectlayer 108, which may otherwise cause some of the light 118 a and 118 bto be scattered or obstructed, as noted above.

After passing through the light pipes 116 a and 116 b, the light 118 aand 118 b strikes the photodetectors 114 a and 114 b, which may beconfigured to detect the light 118 a and 118 b. The photodetectors 114 aand 114 b convert the light energy of the light 118 a and 118 b intoelectrical energy. This electrical energy is passed to themetal-interconnect layer 108 via a metal-oxide-semiconductorfield-effect transistor (e.g., MOSFET 120), which drives the electricalenergy to one or more processors or other components (not shown) thatconvert the electrical energy into a digital signal that may be combinedwith other digital signals to form a digital image. Generally described,each of the photodetectors 114 a and 114 b may correspond with adifferent sensor element in the FSI image sensor 100. As such, the FSIimage sensor 100 illustrated in FIG. 1A may be characterized as showingtwo sensor elements corresponding to the photodetectors 114 a and 114 b.

The photodetectors 114 a and 114 b are included or embedded in anepitaxial layer 104. The epitaxial layer 104 is typically made fromgallium nitride, or some combination of gallium, indium, aluminum,nitrogen, phosphorus, or arsenic. In the example illustrated in FIG. 1A,the epitaxial layer 104 is formed on top of the substrate layer 102through the process of epitaxy growth from the substrate layer 102. Thesubstrate layer 102 may be made from various semiconductor materials,such as crystalline silicon. In some instances, the epitaxial layer 104is made from the same or another material as the substrate layer 102. Insome instances, the epitaxial layer 104 may be a boron-doped, p-typesemiconductor material.

FIG. 1B is a side view of a cross-section of an example of an embodimentof a BSI image sensor 150 that illustrates certain features. In theillustrated example, the BSI image sensor 150 includes a dummy substratelayer 152, a metal-interconnect layer 154, an epitaxial layer 156, oneor more color filters 158 a and 158 b, and one or more micro-lenses 160a and 160 b. These components of the BSI image sensor 150 may be similarto and may be used for similar purposes to the components described withreference to the FSI image sensor 100. However, unlike FSI image sensors(e.g., the FSI image sensor 100) that require light to pass through ametal-interconnect layer, the BSI image sensor 150 may be configured tosense light without the light passing through the metal-interconnectlayer 154.

Specifically, in the example illustrated in FIG. 1B, light 164 a and 164b may be received from the top of the BSI image sensor 150. As describedwith reference to the FSI image sensor 100, the light 164 a and 164 bmay pass, respectively, through the micro-lenses 160 a and 160 b, whichmay focus the light 164 a and 164 b, and through color filters 158 a and158 b, which may filter out certain colors or wavelengths in the light164 a and 164 b. However, in contrast to the above description of theFSI image sensor 100, the light may pass through the color filters 158 aand 158 b and may be received by the photodetectors 162 a and 162 bembedded in the epitaxial layer 156. As such, the light 164 a and 164 bmay be sensed by the photodetectors 162 a and 162 b without having topass through a metal-interconnect layer 154, which may be positionedunderneath the epitaxial layer 156 and may be in electrical contact withthe epitaxial layer 156 via a MOSFET 166.

The epitaxial layer 156 of the BSI image sensor 150 may be similar tothe epitaxial layer 104 of the FSI image sensor 100, except theepitaxial layer 156 may have been grinded (thinned) such that lightentering from the top of the BSI image sensor 150 strikes a lightreceiving surface without passing through the metal-interconnect layer154. Because light does not pass through the wiring in the BSI imagesensor 150, light is not scattered or obstructed to the same degree asobserved in the FSI image sensor 100. Further, due to the position ofthe photodetectors 162 a and 162 b above the metal-interconnect layer154, the BSI image sensor 150 may not require light pipes to channel thelight deeper into the BSI image sensor 150, in contrast to the FSI imagesensor 100 as described above. Thus, the BSI image sensor 150 maygenerally experience better performance when detecting visible lightthan FSI image sensors. However, as noted above, the thin configurationthat enables the BSI image sensor 150 to capture visible lighteffectively also results in impairment in the ability of the BSI imagesensor 150 to capture NIR or IR light as well as the FSI image sensor100. Specifically, because the epitaxial layer 156 of the BSI imagesensor 150 is thinner than the epitaxial layer 104 of the FSI imagesensor 100, the BSI image sensor 150 is not able to detect NIR or IRlight as well as the FSI image sensor 100 due to the relatively longerwavelengths of NIR/IR light.

Various embodiments described herein are directed to an image sensorthat improves on the capabilities of conventional BSI and FSI imagesensors by achieving superior visible-light detection abilities of a BSIimage sensor and, at the same time, the relatively superior NIR/IR lightdetection abilities of an FSI image sensor. In particular, the imagesensor may include certain features similar to a BSI image sensor and aFSI image sensor (or two FSI image sensors), as well as additionalfeatures, in a single image sensor,

FIG. 2 illustrates a side view of a cross-section of an example imagesensor 200. Generally described, the image sensor 200 may represent acombination of some aspects of a BSI image sensor and an FSI imagesensor, whereby components corresponding to a BSI image sensor (e.g., aBSI portion 220) are positioned on top of components corresponding to aFSI image sensor (e.g., an FSI portion 222). Thus, for ease ofreference, the image sensor 200 may be described with reference to or asincluding some components discussed with reference to the FSI imagesensor 100 and the BSI image sensor 150, according to some embodiments.

The image sensor 200 may include the micro-lenses 160 a and 160 b andthe color filters 158 a and 158 b. As described (e.g., with reference toFIG. 1B), the micro-lenses 160 a and 160 b may focus light 230 a and 230b entering the top of the image sensor 200, and the color filters 158 aand 158 b may selectively filter out certain colors of light. The BSIportion 220 of the image sensor 200 may include the epitaxial layer 156,which may have been grinded or thinned to a thickness that is suitablefor receiving visible light. For example, the epitaxial layer 156 mayhave a thickness of approximately three to five micrometers. Theepitaxial layer 156 may include the photodetectors 162 a and 162 b,which may be configured to receive the light 230 a and 230 b that haspassed through the micro-lenses 160 a and 160 b and the color filters158 a and 158 b. As discussed (e.g., with reference to FIG. 1B), thephotodetectors 162 a and 162 b may be included or embedded in theepitaxial layer 156, and the epitaxial layer 156 may be in electricalcontact with a combined metal-interconnect layer 202 via the MOSFET 166.

In some embodiments, the combined metal-interconnect layer 202 of theimage sensor 200 may be fabricated by affixing or bonding the bottom ofa metal-interconnect layer of a BSI image sensor to the top of ametal-interconnect layer of an FSI image sensor. For example, the bottomof the metal-interconnect layer 154 of the BSI image sensor 150 (FIG.1B) may be physically joined or coupled to the top of themetal-interconnect layer 108 of the FSI image sensor (FIG. 1A) to formthe combined metal-interconnect layer 202. However, unlike themetal-interconnect layer 154 of the BSI image sensor 150 (e.g., asdescribed with reference to FIG. 1B), the combined metal-interconnectlayer 202 may include embedded light pipes 206 a and 206 b to enable thelight 230 a and 230 b—particularly IR or NIR light—to pass through theBSI portion 220 of the combined metal-interconnect layer 202 and tocontinue traveling into the FSI portion 222 of the image sensor 200.

In some embodiments, the FSI portion 222 of the image sensor 200 mayinclude a bottom portion of the combined metal-interconnect layer 202,which may correspond to a metal-interconnect layer of an FSI imagesensor (e.g., the metal-interconnect layer 108 as described withreference to FIG. 1). As such, the bottom portion of the combinedmetal-interconnect layer 202 may include the light pipes 116 a and 116b, which may allow the light 230 a and 230 b to pass through the lightpipes 206 a and 206 b in the top portion of the combinedmetal-interconnect layer 202 and to continue on through the bottomportion of the combined metal-interconnect layer 202. The light 230 aand 230 b may then strike the photodetectors 114 a and 114 b that areincluded or embedded in the epitaxial layer 104. Further, the epitaxiallayer 104 may be formed from or coupled to the substrate layer 102, asdescribed (e.g., with reference to FIG. 1A).

As described above, the BSI portion 220 of the image sensor 200 may becharacterized as having two sensor elements corresponding with at leastthe two photodetectors 162 a and 162 b. Similarly, the FSI portion 222of the image sensor 200 may also be characterized as having two sensorelements corresponding with at least the two photodetectors 114 a and114 b. In some embodiments, the sensor elements of the BSI portion 220and corresponding sensor elements of the FSI portion 222 may be aligned.In particular, in such embodiments, the photodetectors 114 a, 114 b, 162a, and 162 b and the light pipes 116 a, 116 b, 206 a, and 206 b of theBSI portion 220 and the FSI portion 222 may be aligned to allow thelight 230 a and 230 b to pass through both portions 220 and 222. Forexample, the photodetector 162 a of the BSI portion 220 may be alignedwith the photodetector 114 a of the FSI portion 222, and the light pipe206 a of the BSI portion 220 may also be aligned with the light pipe 116a of the FSI portion in order to enable light 230 a to be captured byboth photodetectors 114 a and 162 a.

FIG. 3 illustrates a blown-up, cross-sectional view of the image sensor200 described with reference to FIG. 2. Particularly, the illustratedportion of the image sensor 200 may focus on a single sensor element ofthe image sensor 200 illustrated in FIG. 2. In some embodiments, theimage sensor 200 may be configured to leverage the presence ofphotodetectors in the BSI portion 220, as well as photodetectors in theFSI portion 222, to effectively capture both visible light and IR/NIRlight.

In the example illustrated in FIG. 3, both IR/NIR light 306 and 308 andvisible light 302 and 304 may enter from the top of the image sensor 200and may pass through the micro-lens 160 a and the color filter 158 a(e.g., as described with reference to FIG. 2). Due to the shorter wavelength of the visible light 302 and 304, the epitaxial layer 156 of theimage sensor 200 is ground down to a thickness (e.g., three to fivemicrometers in thickness) to facilitate the capture of the visible light302 and 304 by the photo detector 162 a. As such, the photodetector 162a may convert the visible light 302 and 304 into an electrical signalthat is sent to the combined metal-interconnect layer 202. Theelectrical signal may pass through the combined metal-interconnect layer202 to processing resources (not shown) that may convert the electricalsignal into a digital signal. This digital signal may be combined withother digital signals, such as from other sensor elements in the imagesensor 200, to form a digital image.

However, because the wavelengths of the IR/NIR light 306 and 308 arelonger than the visible light 302 and 304, the IR/NIR light 306 and 308may pass through the photodetector 162 a without being detected by thephotodetector 162 a. Instead, the IR/NIR light 306 and 308 may continuetraveling through the light pipes 206 a and 116 a embedded in thecombined metal-interconnect layer 202. In some embodiments, the lightpipes 206 a and 116 a may be configured to control the directionality ofthe IR/NIR light 306 and 308 in order to reduce signal cross talkbetween sensor elements.

After passing through the light pipes 206 a and 116 a, the IR/NIR light306 and 308 may strike the photodetector 114 a in the FSI portion 222 ofthe image sensor 200. In some embodiments, the thickness of thephotodetector 114 a may be configured to be thick enough to ensure thatthe IR/NIR light 306 and 308 will be captured/detected. For example, theepitaxial layer 104 may be configured to have a thickness of eight totwenty micrometers. Further, while the photodetector 116 a is describedas capturing the IR/NIR light 306 and 308, in some embodiments, thephotodetector 116 a may also capture visible light that has passedthrough the photodetector 162 a. The photodetectors 114 a-b may captureand convert at least a portion of the IR/NIR light 306 and 308 into anelectrical signal, which is sent through the MOSFET 120 into thecombined metal-interconnect layer 202 and driven to processing resources(now shown). These processing resources may convert the electricalsignal into a digital signal that may be combined with other digitalsignals from other image sensors to create a digital image.

In some embodiments, the signals generated from the photodetector 162 aand the photodetector 114 a may be combined to increase the quality ofthe digital signal that is ultimately generated from these signals. Inparticular, because the photodetector 162 a may be configured to beparticularly sensitive to the visible light 302 and 304, and because thephotodetector 114 a may be positioned within the image sensor 200 toeffectively sense the IR/NIR light 306 and 308, signals representingboth visible and NIR/IR light from these photodetectors 114 a and 162 amay be combined and converted into a digital image. This digital imagemay reflect a better representation of both visible light information(e.g., day vision) and NIR/IR light information (e.g., night vision)than digital images generated using only one image sensor. Also, becauseboth of the photodetectors 162 a and 114 a are detecting light from thesame source, the image sensor 200 may effectively be able to capturetwice the amount of light as a conventional image sensor. As a result,the image sensor 200 may generate more information using smallerphotodetectors.

Further, in addition to reducing signal cross talk betweenphotodetectors, the light pipes 206 a and 116 a may be configured tokeep the corresponding photodetectors in the FSI and BSI portions 220and 222 of the image sensor 200 aligned. In particular, the light pipes206 a and 116 a may be configured to enable light that has passedthrough the photodetector 162 a to reach the photodetector 114 a. As aresult, the resulting electrical signal that photodetectors 114 a and162 a generate may correspond to light received from the same source,which may improve the overall quality of digital images generated fromthese electrical signals.

FIGS. 4A-4F are component diagrams illustrating a process 400 forfabricating an image sensor (e.g., the image sensor 200 described withreference to FIGS. 2 and 3), according to some embodiments. In suchembodiments, the image sensor may be assembled at least in part byconfiguring and combining a first sensor portion and a second sensorportion.

With reference to FIG. 4A, a first sensor portion 401 a and a secondsensor portion 401 b may be obtained in block 450. In some embodiments,each of the image sensors portions 401 a and 401 b may include asubstrate layer coupled to an epitaxial layer having one or morephotodetectors. In the example illustrated in FIG. 4A, the first sensorportion 401 a may include a substrate layer 102 a and the epitaxiallayer 104 a that includes the photodetectors 114 e and 114 f. Similarly,the second sensor portion 401 b may include a substrate layer 102 b andan epitaxial layer 104 b that includes photodetectors 114 c and 114 d.The substrate layers 102 a and 102 b may correspond to or may havesimilar structure and capabilities as the substrate layer 102 (e.g., asdescribed with reference to FIG. 1A). Similarly, the epitaxial layers104 a and 104 b may correspond to the epitaxial layer 104, as describedabove. Further, the photodetectors 114 c-f may also correspond to thephotodetectors 114 a and 114 b (e.g., as described with reference toFIG. 1A). In some embodiments, each of the first and second sensorportions 401 a and 401 b may be suitable for use as an FSI image sensor.Alternatively, one or both of the first and second sensor portions 401 aand 401 b may be configured for use as a BSI image sensor.

In block 452, a MOSFET 120 a may be coupled to the first sensor portion401 a, and a MOSFET 120 b may be coupled to the second sensor portion401 b. In some embodiments, the operations of coupling an image sensorwafer with a MOSFET, as performed in block 452, may include depositing alayer of silicon (e.g., metal silicon or polycrystalline silicon) on topof the epitaxial layer.

Continuing with the description of the process 400 in FIG. 4B, ametal-interconnect layer 108 a and a metal-interconnect layer 108 b maybe respectively formed on the first sensor portion 401 a and the secondsensor portion 401 b, in block 454. In some embodiments, each of themetal-interconnect layers 108 a and 108 b may be in electrical contactwith the MOSFETs 120 a and 120 b on each respective image sensor wafer.In some embodiments, the MOSFETs 120 a and 120 b may correspond to orfulfill functions similar to those functions described with reference tothe MOSTFET 120 (e.g., as described with reference to FIG. 1A).Similarly, the metal-interconnect layers 108 a and 108 b may beconfigured similarly to the metal-interconnect layer 108 (e.g., asdescribed with reference to FIG. 1A). As such, the MOSFETs 120 a and 120b, respectively, may be coupled to the epitaxial layers 104 a and 104 band may be configured to transfer electrical signals generated by thephotodetectors 114 c-f to the metal-interconnect layers 108 a and 108 b.Further, the metal-interconnect layers 108 a and 108 b may be configuredto drive these electrical signals to processing components in electricalcontact with the metal-interconnect layers 108 a and 108 b (notshown)—e.g., a central processing unit or digital signal processor on animage processing device—where those electrical signals are convertedinto a digital signals and ultimately combined with other digitalsignals to generate a digital image.

In block 456, light pipes 116 e and 116 f may be formed in themetal-interconnect layer 108 a of the first sensor portion 401 a, andlight pipes 116 c and 116 d may be formed in the metal-interconnectlayer 108 b of the second sensor portion 401 b. As discussed (e.g., withreference to the light pipes 116 a and 116 b of FIGS. 1A and 2), thelight pipes 116 e-f and 116 c-d may be configured to guide light throughthe metal-interconnect layers 108 a and 108 b, respectively, therebyreducing the likelihood that the light will be obstructed or scatteredby wires or metal components within the metal-interconnect layers 108 aand 108 b. As further described herein, the light pipes 116 e-f and 116c-d formed in each of the first and second sensor portions 401 a and 401b may be configured to enable light (e.g., NIR or IR light) to passthrough the photodetectors 114 c-d within the second sensor portion 401b, through the metal-interconnect layers 108 a and 108 b, and into thephotodetectors 114 e-f included in the first sensor portion 401 a.

In some embodiments, by configuring the first sensor portion 401 a andthe second sensor portion 401 b via the operations performed in blocks450-456, the first sensor portion 401 a and the second sensor portion401 b may individually be ready to combine into a single, combinedsensor image, as further described with reference to the process 400 asillustrated in FIG. 4C. The first sensor portion 401 a and the secondsensor portion 401 b may be positioned relative to one another inpreparation of coupling the image sensors portions 401 a and 401 btogether. Specifically, in block 458, the first sensor portion 401 a andthe second sensor portion 401 b may be positioned relative to oneanother such that the light pipes 116 e-f of the first sensor portion401 a are aligned with the light pipes 116 c-d of the second sensorportion 401 b. In the example illustrated in FIG. 4C, the light pipes116 c and 116 e may be aligned or oriented about an axis 407 a, and thelight pipes 116 d and 116 f may be similarly aligned or oriented aboutan axis 407 b. The light pipes 116 c-f may be aligned in such a way asto enable light to pass from the second sensor portion 501 b, throughthe metal-interconnect layers 108 a and 108 b via the aligned lightpipes 116 c-f, and finally to the first sensor portion 401 a. Thus, insome embodiments in which the light pipes are cylindrical, the lightpipe 116 c may have the same or a substantially similar diameter to thediameter of the light pipe 116 e, and the light pipe 116 d may have thesame or a substantially similar diameter to the diameter of the lightpipe 116 f.

In block 460, the photodetectors 114 c-d of the second sensor portion401 b may be aligned with the photodetectors 114 e-f. For example, thephotodetector 114 e of the second sensor portion 401 b may be alignedwith the photodetector 114 c of the first sensor portion 401 a, withreference to the axis 407 a. Similarly, the photodetector 114 d of thesecond sensor portion 401 b may be aligned with the photodetector 114 fof the first sensor portion 401 a (e.g., with respect to the axis 407b). In some embodiments, the operations for aligning the photodetectors114 c-f may be accomplished at the same time that the light pipes 116c-f are aligned, as described with reference to the operations of block458.

Turning to FIG. 4D, once the first sensor portion 401 a and the secondsensor portion 401 b are aligned, the image sensors portions 401 a and401 b may be combined to form an image sensor 475. Particularly, inblock 462, the metal-interconnect layer 108 a of the first sensorportion 401 a may be physically coupled to the metal-interconnect layer108 b of the second sensor portion 401 b to form a combinedmetal-interconnect layer 202 a, which may correspond to the combinedmetal-interconnect layer 202 described above (e.g., with reference toFIG. 2). The metal-interconnect layer 108 a may be bonded to themetal-interconnect layer 108 b such that the light pipes 118 c-f andphotodetectors 116 c-f are aligned (e.g., as described with reference toFIG. 4C). Further, in some embodiments, the metal-interconnect layers108 a-b may be physically coupled together such that themetal-interconnect layers 108 a-b are in electrical contact. In suchembodiments, the combined metal-interconnect layer 202 a may function asdriving circuitry for driving electrical signals received from both thephotodetectors 114 c-d, as well as the photodetectors 114 e-f. In someembodiments, coupling the metal-interconnect layers 108 a and 108 b maycause the light pipes 116 c and 116 e and the light pipes 116 d and 116f to touch physically. As such, in embodiments in which the light pipesc-f are made of hollow material having reflective linings, coupling themetal-interconnect layers 108 a and 108 b may cause the light pipes 116c and 116 e and the light pipes 116 d and 116 f to form respectivecavities (e.g., with respect to common axes 407 a and 407 b). In someembodiments in which the light pipes 116 c-f are made of transparent andsolid materials, coupling the metal-interconnect layers 108 a and 108 bmay not cause the light pipes 116 c-f to form cavities.

Once the metal-interconnect layers 108 a and 108 b are physicallycoupled together, the first and second sensor portions 401 a and 401 bmay form the core components of the image sensor 475. However, in orderto be able to receive and detect light, the image sensor 475 may befurther configured as discussed with reference to FIG. 4E. Inparticular, in block 464, the thickness of the second sensor portion 401b, as part of the image sensor 475, may be reduced by performingbackside thinning or grinding. In particular, the substrate layer 102 bmay be removed and the epitaxial layer 104 b may be thinned (e.g., to athickness of approximately three to five micrometers).

As a result of reducing the thickness of the second sensor portion 401 bportion of the image sensor 475, the second sensor portion 401 b may beable to receive and detect light in a manner similar to the manner inwhich a BSI image sensor detects light (e.g., as described withreference to the BSI image sensor 150 of FIG. 1B). For example (e.g., asdescribed with reference to FIG. 2), light (not shown) may enter thesecond sensor portion 401 b from the top of the image sensor 475. Thelight may be received/detected by the photodetectors 114 c-114 d beforeat least a portion of the light (e.g., NIR or IR light) passes throughthe combined metal-interconnect layer 202 a to be received/detected bythe photodetectors 114 e-f of the first sensor portion 401 a of theimage sensor 475. As such, the first sensor portion 401 a may beconfigured to function within the image sensor 475 in a manner similarto an FSI image sensor. In some embodiments of the operations performedin block 464, the thickness of the second sensor portion 401 b may bereduced to approximately three micrometers.

Turning to FIG. 4F, the image sensor 475 may be further configured bycoupling one or more color filters to the second sensor portion 401 b.Specifically, in the example illustrated in FIG. 4F, color filters 110 cand 110 d may be coupled to the top of the second sensor portion 401 b.In some embodiments, the color filters 110 c and 110 d may correspondwith or may functional similarly to the color filters 110 a and 110 b(e.g., described with reference to FIG. 1A). As such, the color filters110 c and 110 d may filter out or prevent certain wavelengths of lightfrom passing through the image sensor 475. Further, in block 468,micro-lenses 112 c and 112 d may be coupled to the one or more colorfilters 110 c and 110 d coupled to the second sensor portion 401 b inblock 466, and the process 400 may end. In some embodiments, themicro-lenses 112 c and 112 d may focus light that enters from the top ofthe image sensor 475 (e.g., as described with reference to themicro-lenses 112 a and 112 b of FIG. 1A).

FIG. 5 illustrates a top view of the image sensor 475, according to someembodiments. In particular, the image sensor 475 may be arranged as a2×2 array of sensor elements 502 a, 502 b, 502 c, and 502 d. In someembodiments, the array of sensor elements 502 a-d may correspond withone of various color filter arrays or color filter mosaics formed byselectively placing certain color filters on each of the cells in thearray. For example, the array of sensor elements 502 a-502 d maycorrespond to a Bayer filter in which the sensor elements 502 a and 502d include a color filter that selectively allows only light in the greenspectrum to pass through, the sensor cell 502 b may selectively allowonly light in the red, NIR, or IR spectrum to pass through, and thesensor cell 502 c may selectively allow only light in the blue spectrumto pass through. Alternatively, the sensor elements 502 a, 502 b, 502 c,and 502 d may be configured with a different color filter array, such asa cyan-yellow-yellow-magenta (CYYM) filter. Further, as described above,each of the sensor elements 502 a-502 d of the image sensor 475 maycorrespond with at least one photodetector included in the second sensorportion 401 b and a corresponding photodetector included in the firstsensor portion 401 a.

While the image sensor 475 is illustrated in FIG. 5 as having a 2×2array of sensor elements 502 a-502 d, the image sensor 475 may beconfigured with an arbitrary number of one or more sensor elementsarranged in a two-dimensional array of sensor elements. For example, theimage sensor 475 may include a 1×1, 640×480, or 4000×3000 matrix ofsensor elements.

FIGS. 6A and 6B illustrate cross-sectional side-views of first sensorportion 600 and a second sensor portion 650 with alternativeconfigurations, according to some embodiments. In particular, thealternative configurations of the first sensor portion 600 and thesecond sensor portion 650 may correspond to use of multiple epitaxiallayers to extend the sensitivity of the photodetectors in those imagesensors to NIR and IR light.

With reference to FIG. 6A, the alternative first sensor portion 600 mayinclude a substrate layer 602 (e.g., similar to the substrate layer 102as described with reference to FIG. 1A). The alternative first sensorportion 600 may further include multiple graded epitaxial layers 604grown from the substrate layer 602, with each layer of the multiplegraded epitaxial layers 604 having a different doping concentration. Inparticular, layers of the multiple graded epitaxial layers 604 closer tothe top of the alternative first sensor portion 600 may have a lowerdoping concentration than layers closer to the bottom of the alternativefirst sensor portion 600. In a non-limiting example, the first sensorportion may be made from a boron-doped, p-type semiconductor material.Accordingly, in this example, a layer of the multiple graded epitaxiallayers 604 closest to the top of the alternative first sensor portion600 may have a boron-doping concentration of approximately 2*10¹⁴/cm³.In contrast, a layer of the multiple graded epitaxial layers 604 nearestthe bottom of the alternative first sensor portion 600 may have arelatively higher boron-doping concentration of approximately2*10¹⁶/cm³.

Differences in the doping concentrations of the multiple gradedepitaxial layers 604 may affect the light detecting capabilities ofphotodetectors included within these layers 604. As such, in someembodiments, the photodetectors 602 a and 602 b of the alternative firstsensor portion 600 may be included within layers having a relativelyhigher doping concentration because layers with higher dopingconcentrations may improve the ability of the photodetectors to detectlight (e.g., NIR or IR light).

With reference to FIG. 6B, the alternative second sensor portion 650 mayalso include a substrate layer 652 and multiple graded epitaxial layers654 grown from the substrate layer 652. As discussed with reference tothe multiple graded epitaxial layers 604, each layer of the multiplegraded epitaxial layers 654 may have a different doping concentration.In particular, layers of the multiple graded epitaxial layers 654 closerto the top of the alternative second sensor portion 650 may have ahigher doping concentration than layers closer to the bottom of thealternative second sensor portion 650. For example, the alternativesecond sensor portion 650 may be a boron-doped, p-type semiconductor. Alayer of the multiple graded epitaxial layers 654 closest to the top ofthe alternative second sensor portion 650 may have a boron-dopingconcentration of approximately 2*10¹⁶/cm³, whereas a layer of themultiple graded epitaxial layers 654 nearest the bottom of thealternative second sensor portion 650 may have a boron-dopingconcentration of approximately 2*10¹⁴/cm³.

As discussed above (e.g., with reference to FIG. 6A), differences in thedoping concentrations of the multiple graded epitaxial layers 654 mayaffect the light detecting capabilities of photodetectors includedwithin these layers 604. As a result, the photodetectors 652 a and 652 bof the alternative second sensor portion 650 may be included withinlayers of the multiple graded epitaxial layers 654 having a relativelyhigher doping concentration due to the improved the ability of thephotodetectors to detect light (e.g., NIR or IR light).

In some embodiments, the alternate first sensor portion 600 and thesecond sensor portion 650 may be combined to form a combine imagesensor, such as by performing the process 400 (e.g., as described abovewith reference to FIGS. 4A-4F) using the alternative first and secondsensor portions 600 and 650 rather than the first and second sensorportions 401 a and 401 b. In such embodiments, the operations performedin the process 400 described with reference to the first sensor portion401 a may instead be performed on the alternative first sensor portion600. Similarly, operations performed in the process 400 described withreference to the second sensor portion 401 b may be performed on thealternative second sensor portion 650. In such embodiments, thegradation of the multiple graded epitaxial layers 654 may be inverted inrelation to the gradation of the multiple graded epitaxial layers 604because the substrate layer 652 and, potentially, some of the epitaxiallayers closer to the bottom of the alternative second sensor portion 650may be grinded down or removed as part of combining the alternativefirst and second sensor portions 600 and 650 to combine a combine imagesensor (see, e.g., operations performed in block 464 of the process 400described with reference to FIG. 4E).

FIG. 7 depicts a general architecture of the image processing device 700that includes an image sensor 718, according to various embodiments. Thegeneral architecture of the image processing device 700 depicted in FIG.7 includes an arrangement of computer hardware and software componentsthat may be used to implement aspects of the present disclosure. Theimage processing device 700 may include many more (or fewer) elementsthan those shown in FIG. 7. It is not necessary, however, that all ofthese generally conventional elements be shown in order to provide anenabling disclosure.

As illustrated, the image processing device 700 may include a processingunit 704, an optional network interface 706, an optional computerreadable medium drive 708, an input/output device interface 710, anoptional display 720, and an optional input device 722, all of which maycommunicate with one another by way of a communication bus 723. Thenetwork interface 706 may provide connectivity to one or more networksor computing systems. For example, the processing unit 704 may receiveand/or send information and instructions from/to other computing systemsor services via one or more networks (not shown). The processing unit704 may also communicate to and from a memory 712 and may furtherprovide output information for the optional display 720 via theinput/output device interface 710. The optional display 720 may beexternal to the image processing device 700 or, in some embodiments, maybe part of the image processing device 700. The display 720 may comprisean LCD, LED, or OLED screen, and may implement touch sensitivetechnologies. The input/output device interface 710 may also acceptinput from the optional input device 722, such as a keyboard, mouse,digital pen, microphone, touch screen, gesture recognition system, voicerecognition system, or another input device known in the art.

The memory 712 may include computer- or processor-executableinstructions (grouped as modules or components in some embodiments) thatthe processing unit 704 may execute in order to various operations. Thememory 712 may generally include random-access memory (“RAM”), read-onlymemory (“ROM”), and/or other persistent, auxiliary, or non-transitorycomputer-readable media. The memory 712 may store an operating system714 that provides computer program instructions for use by theprocessing unit 704 in the general administration and operation of theimage processing device 700. The memory 712 may further include computerprogram instructions and other information for implementing aspects ofthe present disclosure. In addition, the memory 712 may communicate withan optional remote data store 724.

In some embodiments, the memory 712 may store or include digitalrepresentations of images 716 obtained on the image processing device700. In some embodiments, the images 716 stored in the memory 712 mayinclude images captured using an image sensor 718 (e.g., the imagesensor 202 described with reference to FIG. 2). The image sensor 718 mayconvert visible, NIR, or IR light into a digital signal, which may bestored as one or more images in the memory 712. The images may be storedin one or more image file formats, such as a bitmap or raster format(e.g., JPEG, GIF, and BMP) or as vector graphic formats (e.g., scalablevector graphics or “SVG” format). In some embodiments, the images 716may include images received over a network (not shown) via the networkinterface 706. In such examples, the images 716 may include image filesreceives from a website, from a network device, or from an optionalremote data store 724.

In some embodiments, the processing unit 704 may utilize theinput/output device interface 710 to display or output an image on thedisplay 720. For example, the processing unit 704 may cause theinput/output device interface 710 to display one of the images 716 for auser of the image processing device 700.

The detailed description is directed to certain specific embodiments ofthe invention. However, the invention can be embodied in a multitude ofdifferent ways. It should be apparent that the aspects herein may beembodied in a wide variety of forms and that any specific structure,function, or both being disclosed herein is merely representative. Basedon the teachings herein one skilled in the art should appreciate that anaspect disclosed herein may be implemented independently of any otheraspects and that two or more of these aspects may be combined in variousways. For example, an apparatus may be implemented or a method may bepracticed using any number of the aspects set forth herein. In addition,such an apparatus may be implemented or such a method may be practicedusing other structure, functionality, or structure and functionality inaddition to, or other than one or more of the aspects set forth herein.

It is to be understood that not necessarily all objects or advantagesmay be achieved in accordance with any particular embodiment describedherein. Thus, for example, those skilled in the art will recognize thatcertain embodiments may be configured to operate in a manner thatachieves or optimizes one advantage or group of advantages as taughtherein without necessarily achieving other objects or advantages as maybe taught or suggested herein.

All of the processes described herein may be embodied in, and fullyautomated via, software code modules executed by a computing system thatincludes one or more computers or processors. The code modules may bestored in any type of non-transitory computer-readable medium or othercomputer storage device. Some or all the methods may be embodied inspecialized computer hardware.

Many other variations than those described herein will be apparent fromthis disclosure. For example, depending on the embodiment, certain acts,events, or functions of any of the algorithms described herein can beperformed in a different sequence, can be added, merged, or left outaltogether (e.g., not all described acts or events are necessary for thepractice of the algorithms). Moreover, in certain embodiments, acts orevents can be performed concurrently, e.g., through multi-threadedprocessing, interrupt processing, or multiple processors or processorcores or on other parallel architectures, rather than sequentially. Inaddition, different tasks or processes can be performed by differentmachines and/or computing systems that can function together.

The various illustrative logical blocks and modules described inconnection with the embodiments disclosed herein can be implemented orperformed by a machine, such as a processing unit or processor, adigital signal processor (DSP), an application specific integratedcircuit (ASIC), a field programmable gate array (FPGA) or otherprogrammable logic device, discrete gate or transistor logic, discretehardware components, or any combination thereof designed to perform thefunctions described herein. A processor can be a microprocessor, but inthe alternative, the processor can be a controller, microcontroller, orstate machine, combinations of the same, or the like. A processor caninclude electrical circuitry configured to process computer-executableinstructions. In another embodiment, a processor includes an FPGA orother programmable device that performs logic operations withoutprocessing computer-executable instructions. A processor can also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration. Although described herein primarily with respect todigital technology, a processor may also include primarily analogcomponents. A computing environment can include any type of computersystem, including, but not limited to, a computer system based on amicroprocessor, a mainframe computer, a digital signal processor, aportable computing device, a device controller, or a computationalengine within an appliance, to name a few.

Conditional language such as, among others, “can,” “could,” “might” or“may,” unless specifically stated otherwise, are otherwise understoodwithin the context as used in general to convey that certain embodimentsinclude, while other embodiments do not include, certain features,elements and/or steps. Thus, such conditional language is not generallyintended to imply that features, elements and/or steps are in any wayrequired for one or more embodiments or that one or more embodimentsnecessarily include logic for deciding, with or without user input orprompting, whether these features, elements and/or steps are included orare to be performed in any particular embodiment.

Disjunctive language such as the phrase “at least one of X, Y, or Z,”unless specifically stated otherwise, is otherwise understood with thecontext as used in general to present that an item, term, etc., may beeither X, Y, or Z, or any combination thereof (e.g., X, Y, and/or Z).Thus, such disjunctive language is not generally intended to, and shouldnot, imply that certain embodiments require at least one of X, at leastone of Y, or at least one of Z to each be present.

The term “determining” encompasses a wide variety of actions and,therefore, “determining” can include calculating, computing, processing,deriving, investigating, looking up (e.g., looking up in a table, adatabase or another data structure), ascertaining and the like. Also,“determining” can include receiving (e.g., receiving information),accessing (e.g., accessing data in a memory) and the like. Also,“determining” can include resolving, selecting, choosing, establishingand the like.

The phrase “based on” does not mean “based only on,” unless expresslyspecified otherwise. In other words, the phrase “based on” describesboth “based only on” and “based at least on.”

Any process descriptions, elements or blocks in the flow diagramsdescribed herein and/or depicted in the attached figures should beunderstood as potentially representing modules, segments, or portions ofcode which include one or more executable instructions for implementingspecific logical functions or elements in the process. Alternateimplementations are included within the scope of the embodimentsdescribed herein in which elements or functions may be deleted, executedout of order from that shown, or discussed, including substantiallyconcurrently or in reverse order, depending on the functionalityinvolved as would be understood by those skilled in the art.

Unless otherwise explicitly stated, articles such as “a” or “an” shouldgenerally be interpreted to include one or more described items.Accordingly, phrases such as “a device configured to” are intended toinclude one or more recited devices. Such one or more recited devicescan also be collectively configured to carry out the stated recitations.For example, “a processor configured to carry out recitations A, B andC” can include a first processor configured to carry out recitation Aworking in conjunction with a second processor configured to carry outrecitations B and C.

It should be emphasized that many variations and modifications may bemade to the above-described embodiments, the elements of which are to beunderstood as being among other acceptable examples. All suchmodifications and variations are intended to be included herein withinthe scope of this disclosure and protected by the following claims.

What is claimed is:
 1. An image sensor, comprising: a lens; a firstsensor portion; and a second sensor portion coupled to the first sensorportion and positioned between the lens and the first sensor portion,wherein: the first sensor portion comprises: a first photodetector; afirst metal-interconnect layer; and a hollow first light pipe, thesecond sensor portion comprises: a second photodetector; a secondmetal-interconnect layer, wherein the second photodetector is positionedbetween the lens and the second metal-interconnect layer; and a hollowsecond light pipe, the first and second light pipe structured andaligned to form a cavity about a common axis, and the firstmetal-interconnect layer is bonded to the second metal-interconnectlayer to form a combined metal-interconnect layer, wherein the cavity isformed within the combined metal-interconnect layer between the firstphotodetector and the second photodetector to allow light to pass fromthe second photodetector, through the combined metal-interconnect layer,and to the first photodetector.
 2. The image sensor of claim 1, whereina thickness of the first sensor portion is at least seven micrometers.3. The image sensor of claim 1, wherein a thickness of the second sensorportion is no more than five micrometers.
 4. The image sensor of claim1, wherein the image sensor further comprises a color filter.
 5. Theimage sensor of claim 1, wherein: the first light pipe is formed withinthe first metal-interconnect layer; and the second light pipe is formedwithin the second metal-interconnect layer.
 6. The image sensor of claim5, wherein the first metal-interconnect layer is bonded to the secondmetal-interconnect layer such that the first photodetector aligns withthe second photodetector about the common axis.
 7. The image sensor ofclaim 6, wherein the first light pipe is aligned with the second lightpipe about the common axis.
 8. The image sensor of claim 1, wherein thelight originates from a common direction.
 9. The image sensor of claim8, wherein the light comprises at least one of near-infrared light orinfrared light.
 10. The image sensor of claim 1, wherein: the firstsensor image further comprises a first plurality of epitaxial layers;each epitaxial layer of the first plurality of epitaxial layers has adistinct doping concentration; and the first plurality of epitaxiallayers is arranged within the first sensor portion based on respectivedoping concentrations of the first plurality of epitaxial layers. 11.The image sensor of claim 10, wherein: the second sensor portion furthercomprises a second plurality of epitaxial layers; each epitaxial layerof the second plurality of epitaxial layers has a distinct dopingconcentration; the second plurality of epitaxial layers is arrangedwithin the second sensor portion based on respective dopingconcentrations of the second plurality of epitaxial layers; and anarrangement of the second plurality of epitaxial layers within thesecond sensor portion is inverse of an arrangement of the firstplurality of epitaxial layers within the first sensor portion.
 12. Animage processing device, comprising: a lens; an image sensor comprising:a first portion of the image sensor comprising: a first photodetector,and a hollow first light pipe; a second portion of the image sensorcoupled to the first portion and positioned between the lens and thefirst sensor portion and comprising: a second photodetector aligned withthe first photodetector about a common axis, and a hollow second lightpipe aligned on a common axis with the first light pipe to form a cavityaround the common axis with the first light pipe; and a combinedmetal-interconnect layer coupled to the first portion of the imagesensor and to the second portion of the image sensor, wherein the cavityis formed within the combined metal-interconnect layer between the firstphotodetector and the second photodetector to allow light to pass fromthe second photodetector, through the combined metal-interconnect layerto the first photodetector, the second photodetector positioned betweenthe lens and the combined metal-interconnect layer; a memory; and aprocessor coupled to the memory and coupled to the image sensor.
 13. Theimage processing device of claim 12, wherein: the first photodetector isconfigured to receive at least a first portion of light from a lightsource; and the second photodetector is configured to receive at least asecond portion of the light from the light source.
 14. The imageprocessing device of claim 13, wherein: the first photodetector isconfigured to convert the first portion of light into a first electricalsignal; the second photodetector is configured to convert the secondportion of the light into a second electrical signal; and the combinedmetal-interconnect layer is configured to drive the first electricalsignal and the second electrical signal to the processor.
 15. The imageprocessing device of claim 14, wherein the image sensor is arranged suchthat, when the second portion of the image sensor is proximal to thelight source, the at least second portion of the light passes throughthe second portion of the image sensor before the at least first portionof the light passes through the first portion of the image sensor. 16.The image processing device of claim 14, wherein: the first portion ofthe light comprises at least one of infrared light or near-infraredlight; and the second portion of the light comprises visible light. 17.The image processing device of claim 14, wherein the memory includesprocessor-executable instructions that, when executed by the processor,cause the processor to perform operations comprising: generating a firstdigital signal from the first electrical signal; generating a seconddigital signal from the second electrical signal; and generating acombined digital signal from the first digital signal and the seconddigital signal.
 18. The image processing device of claim 17, wherein thememory includes processor-executable instructions that, when executed bythe processor, cause the processor to perform operations furthercomprising generating a digital image based at least in part on thecombined digital signal.
 19. The image sensor of claim 1, wherein thecombined metal-interconnect layer configured to receive electronicsignals from the first and second photodetectors.
 20. The image sensorof claim 1, further comprising a first epitaxial layer and a secondepitaxial layer, wherein the first epitaxial layer includes the firstphotodetector, and the second epitaxial layer includes the secondphotodetector.
 21. The image sensor of claim 20, wherein the secondepitaxial layer is positioned between the lens and the second metalinter-connect layer.
 22. The image sensor of claim 21, furthercomprising a substrate positioned immediately below the first epitaxiallayer.
 23. The image sensor of claim 21, wherein the first epitaxiallayer is positioned between the first metal inter-connect layer and thesubstrate.
 24. The image sensor of claim 1, wherein the first and secondmetal-interconnect layers are physically coupled together so as to be inelectrical contact.
 25. The image sensor of claim 1, wherein the firstmetal-interconnect layer directly adjoins the second metal interconnectlayer.
 26. The image processing device of claim 12, wherein the combinedmetal-interconnect layer configured to receive electronic signals fromthe first and second photodetectors.
 27. The image processing device ofclaim 12, further comprising a first epitaxial layer and a secondepitaxial layer, wherein the first epitaxial layer includes the firstphotodetector, and the second epitaxial layer includes the secondphotodetector.
 28. The image processing device of claim 27, wherein thesecond epitaxial layer is positioned between the lens and the combinedmetal inter-connect layer.
 29. The image processing device of claim 27,further comprising a substrate positioned immediately below the firstepitaxial layer.
 30. The image processing device of claim 12, whereinthe first metal-interconnect layer directly adjoins the second metalinterconnect layer.